Renal Regulation of Acid Base Balance - McCormick

Question 1

What effect does chemical buffers have on pH changes?

Answer 1

Minimize, but can’t prevent changes caused by strong acid or base

Question 2

Characteristics of volatile acid

Answer 2

Carbonic acid - H2CO3
CO2 - volatile gas
Pulm ventilation controls H2CO3 in body fluids
From oxidative metabolism

Question 3

Characteristics of fixed acids

Answer 3

Non-carbonic acids - eg. sulfuric, phosphoric
Initially neutralized, ultimately excreted
NOT fixed by ventilation

Question 4

3 Lines of defense against pH changes

Answer 4

1. Chemical buffers - H
   - -can be Hb, bone
2. Respiration - CO2
3. Kidneys - HCO3
   - -major EC buffer

Question 5

Why is bicarbonate buffer system so powerful?

Answer 5

Components are abundant

Open system - HCO3 and CO2 readily adjusted by respiration and renal function

Question 6

Renal response to excess acid

Answer 6

All filtered HCO3 is reabsorbed

Additional H secreted, primarily as NH4

Question 7

Renal response to excess base

Answer 7

Incomplete reabsorption of filtered HCO3
Decreased H secretion
Secretion of HCO3 in CD

Question 8

How is most H secreted?

Answer 8

In combination with urinary buffers

• titratable acid - HPO4 most imp
• ammonia

Question 9

Luminal pH along nephron

Answer 9

GC - 7.4
PT and DT - 6.7
Loop - 7.6
Excreted < 6.0

Question 10

a-intercalated cells

Answer 10

In CD
Actively secrete acid (H)
H-ATPase

Question 11

B-intercalated cells

Answer 11

In CD
Actively secrete base (HCO3)
HCO3-Cl exchanger

Question 12

Acidification in the proximal tubules

Answer 12

Most of the H secreted by PT is used to reabsorb filtered HCO3
-so it only falls slightly to 6.7

Question 13

If arterial pH is too high, what is kidney response

Answer 13

Respond by incompletely reabsorbing HCO3

Normally 80% reabsorbed in PT, remainder in TAL (saturable)

Question 14

What is produced from glutamine oxidation

Answer 14

2 NH4
2 HCO3
-way to excrete H

Question 15

What happens in chronic acidemia (elevated H conc)

Answer 15

Up regulated renal NH4 production and excretion

Question 16

What happens in alkalemia (reduction in H conc)

Answer 16

B-intercalated cells (CD) secrete HCO3

Question 17

6 Factors that control renal H secretion

Answer 17

1. Decreased intracellular pH
2. Increased plasma Pco2
3. Carbonic anhydrase activity
4. Increased Na reabsorption
5. Decreased extracellular K
6. Increased plasma aldosterone

Question 18

What happens from extensive use of diuretics?

Answer 18

ECF contraction - Increased RAAS
Increased tubular secretion of H
Leads to increased reabsorption of all filtered HCO3 and new HCO3
Leads to metabolic alkalosis

Question 19

What type of acid base disturbance is excessive diuretic use?

Answer 19

Metabolic alkalosis

Question 20

Respiratory acidosis

Renal response

Answer 20

Increased arterial Pco2
Renal increases H secretion to restore pH
Also increases HCO3

Question 21

Respiratory alkalosis

Renal response

Answer 21

Decreased arterial Pco2

Renal response leads to less H secretion and more HCO3 excretion

Question 22

Metabolic acidosis

Answer 22

Low plasma pH
Gain of fixed acid or loss of HCO3
BOTH lead to fall in HCO3

Question 23

Respiratory compensation to metabolic acidosis

Answer 23

Increased ventilation

Question 24

Metabolic alkalosis

Answer 24

Abnormally high plasma pH
Excessive gain of strong base or excessive loss of fixed acid (vomit)
Resp compensation - decreased ventilation

Question 25

If you have pH that is acidotic, what would you expect Pco2 to be if respiratory?

Answer 25

Pco2 > 40 mmHg

Question 26

Normal range for anion gap?

Answer 26

8-16 mEq/l

Normal or increased depending on cause of metabolic acidosis

Question 27

Hyperchloremic acidosis

Answer 27

AG unchanged

Loss of HCO3 is matched by gain of Cl-

Question 28

Normochloremic

Answer 28

High anion gap acidosis

HCO3 is replaced by unmeasured anion